Adding a ppa repo and get key signed - no valid OpenPGP data - proxy issue?
Solution 1:
Try
export http_proxy=http://proxy.mycompany.de:3128; export https_proxy=$http_proxy
sudo -E apt-key adv --keyserver keyserver.ubuntu.com --recv-keys A258828C
Try
export http_proxy=http://proxy.mycompany.de:3128; export https_proxy=$http_proxy
sudo -E apt-key adv --keyserver keyserver.ubuntu.com --recv-keys A258828C